Hereinbefore, epoxy resins have been generally and widely used in the fields of, for example, adhesives, paints, coating agents for surface protection. Such epoxy resins, although having an excellent adhesiveness to metals, woods and other materials, have a drawback in that they generally have an inferior impact resistance and, therefore, cracks may be formed upon impact during use, or phenomena such as peel-off may occur. To eliminate these drawbacks and improve other various properties thereof, various compositions comprising polymers having a low glass transition point formulated into epoxy resins have been proposed. For example, Japanese Unexamined Patent Publication (Kokai) No. 54-83097 filed by the present Applicant discloses a composition containing a specific modified low molecular weight polyolefin formulated thereinto, which has an improved water resistance and chemical resistance. However, further research and a development of the improvement in the impact resistance is needed.
On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 51-551 discloses a composition comprising an ethylene copolymer containing an epoxy group. Although the impact resistance of this composition is considerably improved, because of the high molecular weight of the modifier, the problems arise of a compatibility with the epoxy resin, a lowering of workability due to an increased viscosity, and the final appearance of the applied coating.
Also, Japanese Unexamined Patent Publication (Kokai) No. 55-84335 discloses a composition comprising a modified liquid polyisoprene rubber to which maleic anhydride or a derivative thereof is added, an epoxy resin and a curing accelerator. However, under the conditions specifically shown in the Example, the reaction between the modified liquid polyisoprene and the epoxy resin is insufficient and a composition having a poor adhesiveness and impact resistance is produced.
Further, Japanese Unexamined Patent Publication (Kokai) No. 57-98535 discloses an epoxy resin composition containing a maleated polybutadiene and a tertiary amine formulated thereinto, but this is not practical because the surface hardness and heat resistance are greatly reduced.
As described above, in epoxy resin compositions of the prior art, because of the high molecular weight of the modifier which is added to improve the impact resistance, the compatibility with the epoxy resin is generally not good, and an increase of the viscosity occurs when the composition is used in the molten state or the solution state, whereby there arise drawbacks such as the lower workability when formed into conventional paints or adhesives and an inferior appearance of the applied coating when formed into a composition for powdery paint. Furthermore, these epoxy resin compositions cannot be considered to have a satisfactory improvement of the impact resistance, and a further development of the water resistance, rust resistance, oxidation resistance, and chemical resistance, is necessary.